Cells are cultured in specialized cell culture containers including roller bottles, cell culture dishes and plates, multiwell plates, microtiter plates, common flasks and multi-layered cell growth flasks and vessels. Cells in culture attach to and grow on the bottom surface(s) of the flask, immersed in a suitable sustaining media.
Traditional cell culture vessels are constructed with a large internal space (“headspace”) devoted to gas exchange. This headspace creates a requirement for laboratories growing cells in culture to use inverted microscopes to enable cell visualization. The extended optical pathway through a large body of air inside traditional cell culture vessels precludes the use of standard upright microscopes to visualize the cells growing within the traditional vessel. Most cell culture laboratories utilize inverted microscopes to visualize cells in culture.
With the advent of cell-based high-throughput applications, cell culture vessels or devices have been developed to provide an increased surface area for cell growth while also providing necessary gas exchange. These systems also employ traditional cell culture vessels including common flasks, roller bottles, cell culture dishes, as well as multi-layered cell growth vessels including multi-layer flasks, multi-layer cell culture dishes, bioreactors, cell culture bags and the like, which may include specialized surfaces designed to enhance the cell culture parameters including growth density and differentiation factors. For example, Corning Incorporated sells multi-layer cell culture devices such as the HYPERStack® and the HYPERFlask®. See, for example, US Publication No. 2007/0026516. While such multi-layer cell culture devices enable an increased surface area for cells in culture, these multiple layers of cells in culture obstruct the visualization of cells cultured in these devices.
The configuration of multi-layer vessels is very different from traditional cell culture vessels in that the air required for cellular metabolism is obtained through spaces (“tracheal spaces”) beneath each cell growth layer, where each cell growth layer has cell growth surface which is constructed from a gas permeable material. By having an essentially external headspace, the volumetric footprint of the individual cell culture compartments is more compact than those of traditional cell culture vessels. This permits the stacking of many cell culture layers together to provide more surface area than that which is available in traditional cell culture vessels of similar volumetric size. Removal of the headspace permits cell visualization on the top layer using standard upright microscopes that might have enough space between the stage and the objective lenses to position the vessel.
However, the stacking of the cell culture layers in multi-layer vessels does not permit visualization of all the cell culture layers. The design of some multi-layer vessels such as the HYPERStack even prevents visualization of the lowest cell culture layer using an inverted microscope with standard objective lenses.
There is a need for multi-layer cell culture vessels that can engage with a microscope to allow cells to be evaluated microscopically while still in culture in the device.